1. Field of the Invention
This invention relates to hollow fibers for dialysis and to a method for the manufacture thereof. More particularly, this invention relates to hollow fibers for use as a dialysis membrane of an artificial kidney device and to a method for the manufacture thereof. Description of Prior Art:
Recently, use of hollow fibers in a diaphragm for dialysis has come to prevail. Particularly in artificial kidney devices, use of extremely thin hollow fibers for dialysis is gaining in popularity. As concerns hollow fibers for dialysis, various inventions pertaining to materials for forming hollow fibers have been published (e.g., Japanese Patent Publication SHO No. 39(1964)-28,625, USP 3,888,771 (SHO No. 50(1975)-40,168), and SHO No. 55(1980)-1,363, and Japanese Patent Laid-open SHO No. 49(1974)-134,920). These hollow fibers are mostly manufactured by extruding a spinning dope of cuprammonium cellulose into a gaseous atmosphere, allowing extruded tubes of the spinning dope to fall by the force of gravity acting thereon, and thereafter immersing them in a coagulating bath thereby coagulating and regenerating the tubes of the spinning dope. While the tubes are falling down the gaseous atmosphere, the ammonia in the dope is volatilized and released through the surface of the tubes into the atmosphere and, therefore, the tubes begin to solidify inwardly from the surface. The hollow fibers consequently produced invariably form skin layers on their external surface, though to varying degrees depending on the types of method of manufacture. None of the hollow fiber, therefore, has uniform texture throughout the entire wall thickens of their tubes. Hollow Fibers of certain types have been observed to have voids formed in the walls of their tubes. When hollow fibers possessing such skin layers or hollow fibers containing voids in their walls are used for dialysis, especially for dialysis in artificial kidney devices, they are liable to cause thrombosis, impair blood cells and other beneficial components because of the voids, and effect only insufficient separation of components of intermediate molecular weights. Thus, they are not fully effective in dialyzing the fluid under treatment. Further, the conventional hollow fibers are not fully satisfactory in terms of mechanical strength. Any effort to improve hollow fibers in efficiency of dialysis entails the necessity for decreasing their wall thickness at an inevitable sacrifice of mechanical strength. It is well known that the ease of handling of the spinning dope at every step of spinning increases in proportion as the viscosity of the spinning dope decreases. If the viscosity of the spinning dope is excessively lowered, however, the concentration of cellulose in the dope is lowered with the possible result that the hollow fibers consequently produced will suffer from insufficient strength and occurrence of pinholes. The conventional hollow fibers do not tolerate a decrease in the viscosity of the spinning dope.
An object of this invention, therefore, is to provide novel hollow fibers for dialysis and a method for the manufacture thereof.
Another object of this invention is to provide hollow fibers for dialysis so excellent in the effect of dialysis as to warrant utility in artificial kidney devices and a method for the manufacture of the hollow fibers.